sources: factor out Source::URL::Weibo

Additionally, fixed some broken tests and changed normalization for urls
of album type to point to the mobile version instead, because they're
only visible to logged-in users.

app/logical/source/url.rb

@@ -31,6 +31,7 @@ module Source
       Source::URL::Plurk,
       Source::URL::Skeb,
       Source::URL::TwitPic,
+      Source::URL::Weibo,
     ]
 
     # Parse a URL into a subclass of Source::URL, or raise an exception if the URL is not a valid HTTP or HTTPS URL.